Thermally assisted magnetic recording is proposed as a recording method for achieving a recording density of 1 Tb/in2 or more (Jpn. J. Appl. Phys. 38, Part 1, p. 1839 (1999)). Traditional magnetic recording causes thermal fluctuation when the recording density becomes 1 Tb/in2 or more, losing recorded information. Preventing this problem requires increasing the coercivity of the magnetic recording medium. However, there is a limit to the size of a magnetic field that can be generated by the recording head. Excessively increasing the coercivity makes it impossible to form recording bits on the medium. To solve this problem, thermally assisted magnetic recording heats the magnetic recording medium using light at the moment of recording to reduce the coercivity. This makes it possible to record information onto a coercive medium and achieve a recording density of 1 Tb/in2 or more.
In thermally assisted magnetic recording, the spot diameter of applied light must be a size similar to that of a recording bit (several tens of nm). This is because light having a larger spot diameter than a recording bit would erase information in adjacent tracks. For this reason, near-field light is used to heat such a minute region. Near-field light is a local electromagnetic field that is present near a minute object having a length shorter than the optical wavelength (light whose wave number has imaginary components). It is generated using a minute aperture or metallic scatterer having a diameter smaller than the optical wavelength. For example, use of a triangular metallic scatterer as an efficient near-field light generator is proposed (Technical Digest of 6th international conference on near field optics and related techniques, Netherlands, Aug. 27-31, 2000, p. 55). Entry of light into the metallic scatterer excites plasmon resonance in the metallic scatterer, generating intense near-field light at the top of the triangle. Use of this near-field light generator allows light to be efficiently focused on a region having a size of several tens of nm or less.
Japanese Unexamined Patent Publication No. 2006-185548 discloses a thermally assisted magnetic head including a slider and a light source unit. The slider includes a magnetic head portion having an optical waveguide disposed adjacent to an electromagnetic coil element in the layering direction of the magnetic head. The light source unit includes a light source disposed on a light source support substrate which is different from the slider In this configuration, light emitted from the light source is introduced into the optical waveguide and emitted from the light-emitting surface of the optical waveguide in the medium-opposed surface. As a result, the magnetic recording medium can be heated locally.
Japanese Unexamined Patent Publication No. 2009-43377 discloses a thermally assisted magnetic head including a temperature sensor. This thermally assisted magnetic head achieves stable recording by inspecting the temperature of the head before recording.